Apparatus and method for measuring chromatic dispersion by variable wavelength

Abstract

An apparatus and method for characterizing or measuring chromatic dispersion in an optical fiber segment. The fiber is accessed at one end with a signal generator injecting modulating pulsed signals which are reflected at the other end of the fiber, the apparatus determining the phase difference between the modulation signals and the reflected modulation signals and calculating the chromatic dispersion therefrom.

1. An apparatus for measuring the chromatic dispersion of an optical fiber having first and second opposite ends, the apparatus comprising:
 an optical source able to generate optical signals at a variable wavelength; 
 a signal generator able to generate modulation signals; 
 a modulator able to generate modulated signals on the basis of the optical signals and of the modulation signals; 
 a coupling device able to send the modulated signals to the first end of the fiber; 
 an impulse generator in the signal generator and able to generate impulsive electrical signals having variable amplitude and having duration and periodicity determined according to characteristics of the fiber such that the modulated signals are shaped by pulses having variable amplitude; 
 a reflecting element at the second end of the fiber able to reflect the modulated signals and to generate reflected optical signals having a reflected modulated component; and 
 a comparator associated with the first end of the fiber and able to measure a phase difference between the modulation signals and the reflected modulated component. 
 
   
   
     2. The apparatus defined in  claim 1  wherein the coupling device is further able to receive the reflected optical signals and the comparator comprises
 an optical receiver connected to the coupling device and able to convert the reflected optical signals into electrical signals representative of the reflected modulated component; and 
 a phase comparator connected to the signal generator and to the optical receiver and able to generate an electrical signal representative of the phase difference. 
 
   
   
     3. The apparatus defined in  claim 2  further comprising
 a processor associated with the optical source and with the signal generator and able selectively to control the wavelength of the optical signals and the characteristics of the modulation signals. 
 
   
   
     4. The apparatus defined in  claim 3  wherein the processor is further able to calculate the chromatic dispersion of the optical fiber on the basis of the phase difference measured as the wavelength of the optical signal varies. 
   
   
     5. The apparatus defined in  claim 1  wherein the amplitude of the pulses is variable in sinusoidal fashion. 
   
   
     6. The apparatus defined in  claim 1  wherein a duration of the pulses is no greater than twice a time of propagation of the pulses in the fiber. 
   
   
     7. The apparatus defined in  claim 1  wherein a periodicity of the pulses is no less than four times a time of propagation of the pulses in the fiber. 
   
   
     8. A method for measuring the chromatic dispersion of an optical fiber having first and second opposite ends, the method comprising the steps of:
 generating optical signals at variable wavelength; 
 generating modulation signals shaped by impulse electrical signals having predetermined phase, variable amplitude, and duration and periodicity determined according to characteristics of the fiber; 
 modulating the optical signals with the modulation signals such that the optical signals modulated with the modulation signals are shaped by pulses having variable amplitude; 
 sending the modulated signals to the first end of the fiber; 
 reflecting at the second end of the fiber the modulated signals in such a way as to obtain reflected optical signals having a reflected modulated component; 
 measuring at the first end a phase difference between the modulation signal and the reflected modulated component. 
 
   
   
     9. The method as claimed in  claim 8  further comprisign the step of
 calculating a chromatic dispersion of the optical fiber on the basis of a phase difference measured as a wavelength of the optical signals varies. 
 
   
   
     10. The method defined in  claim 8  wherein an amplitude of the pulses is variable in sinusoidal fashion. 
   
   
     11. The method defined in  claim 8  wherein a duration of the pulses is no greater than twice a time of propagation of the pulses in the fiber. 
   
   
     12. The method defined in  claim 8  wherein a periodicity of the pulses is no less than four times a time of propagation of the pulses in the fiber.